Initializing the project

Create app.js in the root folder and include it in the HTML as in

<script src="app.js" type="module"></script>

Open app.js and add:

const $ = function(args){ return document.querySelector(args);}
const $$ = function(args){ return document.querySelectorAll(args);}

HTMLElement.prototype.on = function(a, b, c){ return this.addEventListener(a, b, c); }
HTMLElement.prototype.off = function(a, b){ return this.removeEventListener(a, b); }
HTMLElement.prototype.$ = function(s){ return this.querySelector(s); }
HTMLElement.prototype.$$ = function(s){ return this.querySelectorAll(s); }

Play with the console using $, $$ and direct DOM APIs.